Is Grubee Freewheel Sprocket made for any chain!

Discussion in 'Frame Mounted Engines' started by Irish John, Mar 9, 2009.

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  1. Irish John

    Irish John Guest

    Has anyone else noticed that the 11T Grubee freewheel drive sprocket that comes with the 4-stroke kits never seems to be accurately enough made to fit the 1/2" pitch of a 415 motorcycle chain. It is presumably made for aa 415 chain but the pitch on a normal bicycle chain is also 1/2" or 12.7mm so it should fit. So often the chain wants to ride over the sprocket teeth because the teeth can't find the space between the links and the chain makes a horrible noise when this happens. Recently I put a new Japanese EK chain on a sprocket that's done 4000 kms and even after 260 kms it still doesn't like running over the sprocket. I can't bear hearing a nice new $25 chain being mangled by a badly fitting sprocket.
    My take on this problem is that the sprockets are not accurately machined to begin with but the problem is greatly worsened when the sprocket begins to wear on the leading edge of the teeth - you get a slightly concave face on the teeth. Pity the sprocket isn't reverseable because it could be turned around so the good side of the teeth could be used.
    I reckon that after 4 or 5000 kms any 11T sprocket will wear out and needs to be replaced. Pity the teeth can't be replaced instead of the whole unit but the units aren't too expensive (about Aus $15 each). Replacing the whole sprocket means undoing the gearbox from the engine and it's a lengthy messy job even if it isn't difficult.
    What have other people found with using a good 415 Japanese chain on an older sprocket that's done maybe 4000 kms? Do other people just replace the freewheel every so often or do they just not bother?
    I notice that the Chinese chains have improved in the last year and it's not uncommon now to find that the links are actually equally spaced at the right intervals. 18 months ago most of the chinese chains had variable link lengths which were most noticeable when you held the chain up against a quality Jap one.
    Last edited by a moderator: Mar 9, 2009